A critical step in the fabrication of fiber-reinforced composites is the controlled, uniform positioning of the fiber in the ceramic matrix. These composites are frequently fabricated by infiltrating the fully or partially assembled fibers with molten ceramic matrix material or a suspension of the ceramic matrix material. Such a suspension may be a sol-precursor of the matrix, or a slurry of the matrix powder and a binder solution.
The aforementioned slurry infiltration techniques generally must be carried out by hand and are extremely tedious. In addition, these slurry infiltration techniques impose limits on the size and uniformity of the composite. For example, the uniformity of the composite is often disturbed by a well-known filtration phenomenon which causes the particles of matrix material to be strained from the suspension when they are infiltrating the porous compact.
In order to solve these problems, it has been proposed in "Carbon Fiber Composites With Ceramic and Glass Matrices," Sambell, R. A. J. et al, J. Mater S.C.I. 7, page 767 (1972) to coat fibrous materials with a suspension of matrix particles in a binder solution. In this process, carbon fiber yarn was taken from its spool and, after a heat cleaning step to burn off the sizing, the fiber yarn was drawn through a coating tank containing a suspension of matrix particles in a binder solution, through a drying zone and finally wound around a mandrel. This coating technique works well for fiber yarn but not for monofilaments. The yarn, consisting of a multiplicity of fibers and capillary spaces, provides a wicking action which accepts and retains the coating slurry in the yarn. If this process is applied to smooth monofilament fibers, the coating breaks up into small droplets because of the surface tension of the coating liquid.
In a non-analogous art, it is known to apply ultraviolet curable protective coatings to glass fibers used in fiber optical applications to provide enhanced strength to the fibers. For example, U.S. Pat. No. 4,741,958 issued on May 3, 1988 discloses a buffer-coated and overcoated optical glass fiber in which the top coat has high strength and a high tensile modulus combined with good elongation and solvent resistance. The top coat is applied by ordinary coating procedures and cured by exposure to ultraviolet radiation.
U.S. Pat. No. 4,585,534 issued on Apr. 29, 1986 discloses the application of an ultraviolet-initiated cationically curable liquid coating composition to an optical fiber as a protective coating. The coating is of low modulus.
U.S. Pat. No. 4,662,307 issued on May 5, 1987 discloses a method and apparatus for recoating optical waveguide fibers with an ultraviolet-curable resin. The method involves positioning the fiber in a mold, introducing ultraviolet-curable resin into the mold and introducing ultraviolet light into the mold to cure the resin.
U.S. Pat. No. 4,636,405 issued on Jan. 13, 1987 discloses a curing apparatus for a coated optical fiber. The curing apparatus includes an elongated ultraviolet lamp and an elliptical mirror which focuses the ultraviolet energy onto the coated fiber. The fiber is surrounded by a cylindrical chamber which is transparent to ultraviolet light and includes a jacket for conveying fluid which absorbs infrared energy. A cooling gas flows into the chamber to cool the coated fiber.
Finally, U.S. Pat. No. 4,407,847 issued on Oct. 4, 1983 discloses a process for the manufacture of glass sheets. The process includes the steps of selecting a glass sheet and applying an opaque band to a surface of the sheet. The opaque band is formed from a radiation curable paste which includes a filler material which fuses to the glass sheet when heated to its fusion temperature, and a radiation curable material which is heat decomposable into components which are non-reactive with the glass sheet. After the paste is applied, the radiation curable material is cured to form a temporary bond between the paste and the surface of the glass sheet and heating is continued to fuse the filler material to the glass sheet and at the same time, decompose the radiation curable material into components which are non-reactive with the glass sheet.
Accordingly, there is a need in the art of fiber/matrix composites for a method for coating fibers with a continuous coating of ceramic matrix material in order to facilitate the subsequent fabrication and improve the properties of fiber-reinforced ceramic matrix composites.
Accordingly, it is the primary object of the present invention to provide a process for applying a continuous coating of ceramic matrix material on the surface of a fiber.
It is a still further object of the present invention to provide a process for the preparation of fiber-reinforced ceramic matrix composites which provides more uniform composite materials.
It is a still further object of the present invention to provide a process for the preparation of fiber-reinforced ceramic matrix composites which can be carried out in a continuous manner on an automated apparatus.
It is a still further object of the present invention to provide a method for the preparation of fiber-reinforced ceramic matrix composites which does not impose size limitations on the composites.
These and other objects of the present invention will be apparent to one of ordinary skill in the art from the summary and detailed description which follow.